Process for producing cellulose multi-filament with lower coefficient of variation of section diameter

ABSTRACT

The present invention relates to a cellulose fiber having a highly homogeneous section, particularly to a cellulose fiber with lower Coefficient of Variation of section diameter (CV(%)). Specifically, the present invention relates to a cellulose fiber wherein Coefficient of Variation of section diameter (CV(%)) of a mono-filament constituting a multi-filament prepared by dissolving a cellulose powder in liquid N-methylmorpholine N-oxide (hereinafter referred to “NMMO”) is below 2.5. According to the present invention, a lyocell multi-filament is produced comprising the steps of (i) preparing a spinning solution by homogeneously dispersing, swelling and dissolving cellulose powder in a NMMO solution; (ii) spinning the spinning solution into an air gap through a spinning nozzle; and (iii) coagulating the extruded-spun spinning solution in a coagulation bath. In particular, the coagulating step is adjusted by means of a coagulation coefficient in the range of 0.8 to 1.3 and the coagulation coefficient is expressed as T D /T C , T D =T D +T A  90 and T D  T A  and T c  mean the temperature of a spinning solution, the temperature of cooling air applied in an air gap and the temperature of a coagulation bath, respectively.

TECHNICAL FIELD

The present invention relates to a cellulose fiber having a highly homogeneous section, particularly to a cellulose fiber with lower Coefficient of Variation of section diameter (CV(%)). Specifically, the present invention relates to a cellulose fiber wherein Coefficient of Variation of section diameter (CV(%)) of a mono-filament constituting a multi-filament prepared by dissolving a cellulose powder in liquid N-methylmorpholine N-oxide (hereinafter referred to “NMMO”) is below 2.5.

BACKGROUND ART

A lyocell fiber is made from a spinning solution wherein cellulose is dissolved in NMMO and it has an advantage of having high hygroscopicity, dry and wet strength and modulus. Moreover, unlike viscose rayon, lyocell is recognized as an environmentally-friendly fiber which does not pollute the environment with harmful substances. Such a lyocell fiber, as an alternative of rayon, may be used as a tire-cord and for this purpose, the homogeneity of a section diameter of a mono-filament constituting a multi-filament is necessary to accomplish high strength as a tire-cord material. The homogeneity may be expressed as Coefficient of Variation of section diameter (CV(%)).

International Publication No. WO 2001/86043 discloses lyocell fibers having 6.5% or more in Coefficient of Variation of section diameter (CV(%)). The invention disclosed in WO 2001/86043, however, has an object of increasing Coefficient of Variation of section diameter (CV(%)) and it is not suitable for using as industrial materials, particularly, for tire-cord because it has 0.7 to 5.0 g/d in strength as shown in examples.

Referring to other prior invention, U.S. Pat. No. 6,773,648 discloses a lyocell fiber having 6 to 17% in Coefficient of Variation of section diameter (CV(%)) along fiber and 10 to 22% in Coefficient of Variation of section diameter (CV(%)) between fibers. Those of Coefficient of Variation of section diameter along fiber and between fibers as well, however, are not suitable for using as a lyocell fiber for tire-cord.

DISCLOSURE OF INVENTION Technical Problem

The present invention suggests a method for improving Coefficient of Variation of section diameter by adjusting the temperatures of an air gap and a coagulation bath during the process in order that Coefficient of Variation of section diameter (CV(%)) of a mono-filament constituting a multi-filament is lowered below 2.5.

Technical Solution

It is an object of the present invention to provide a lyocell fiber for using as a high-strength dip cord for tire-cord by adjusting the temperatures of cooling air in the air gap and the coagulation bath and adjusting Coefficient of Variation of section diameter (CV(%)) of mono-filament constituting a multi-filament to below 2.5.

ADVANTAGEOUS EFFECTS

The lyocell fiber according to the present invention may have suitable properties for using as a dip cord for tire cord. According to the present invention, the Coefficient of Variation of section diameter (CV(%)) may be controlled in the desired range by adjusting coagulation coefficient. Hence, the present invention has an advantage of producing a lyocell multi-filament for using as a dip cord for tire-cord.

BEST MODE FOR CARRYING OUT THE INVENTION

Though processes for producing a lyocell fiber have been disclosed in many prior arts, a lyocell fiber having different properties according to each condition of process may be produced. Particularly, the spinning pressure in a spinning nozzle, the diameter and the number of orifice, the spinning speed, the temperature and the air velocity of cooling air in an air gap, and the temperature, the concentration of a coagulation bath are the main factors which determine the properties of a lyocell fiber. The lyocell fiber produced according to the present invention is prepared by controlling conditions of process and thereby having suitable properties for tire-cord.

The properties of the lyocell fiber produced according to the preset invention are influenced not by the above-described factors or others independently, but by the correlation between the factors. The present invention is characterized in that such factors are controlled to have the correlation.

The factors which determine the homogeneity of the produced lyocell fiber may be divided into a cooling condition in an air gap and a coagulating condition. Therefore, the condition factors may be expressed as a coagulation coefficient as a result of a mathematical function of the temperature of the cooling air in the air gap and the temperature of the coagulation bath, as shown below.

Coagulation Coefficient=T _(D) /T _(c)=0.8 to 1.3

(T _(D) =T _(D) +T _(A)−90)

T_(D) means the temperature of a spinning solution, T_(A) means the temperature of cooling air applied in an air gap and T_(c) means the temperature of a coagulation bath.

In the process of producing a lyocell fiber according to the present invention, the coagulation coefficient is adjusted to 0.8 to 1.3. Through the adjustment of the coagulation coefficient, the spinning solution is cooled and the temperature of the spinning solution and the temperature of the coagulation bath are adjusted within a similar temperature range, and then the NMMO contained in the spinning solution is fed into the coagulation bath and spreads slowly therein. In doing so, the homogeneity of a mono-filament may be improved by the lower spreading rate. In order to lower the spreading rate, coagulation coefficient is adjusted in the range of 0.8 to 1.3. Hereinafter, the process for producing a lyocell fiber with lower Coefficient of Variation of section diameter (CV(%)) will be described in detail.

As a raw material of producing a lyocell fiber, a softwood pulp having 800 to 1200 in degree of polymerization and 93% or more in the contents of α-cellulose is pulverized with a crusher into powder with 500 μm in average diameter. An NMMO solution having 10 to 20 wt % in the contents of water is prepared. The pulp powder and the NMMO solution are fed into an extruder at the same time. And then the cellulose powder is evenly dispersed, swollen and dissolved in the NMMO solution within the extruder maintained at the temperature of 90 to 110° C., and then transferred to the spinning nozzle through the spinning line at the temperature of 90 to 110° C. and thereby the spinning solution is prepared. The spinning solution is spun through the spinning nozzle into a filament yarn.

In the process of producing a lyocell fiber according to the present invention, the diameter of the spinning nozzle may be 80 to 130 mm. After the diameter of the spinning nozzle is determined, the number of orifice and the ratio of the length to the diameter (L/D ratio) of orifice may be determined. The number of orifice may be 800 to 1200, the diameter of the orifice may be 800 to 2000 μm, and the L/D ratio of the orifice may be 2 to 5. The spinning solution is extruded-spun into an air gap. The spinning solution is cooled and solidified in order to draw the spinning solution in the air gap, wherein the air is blown at lower temperature in the range of 0 to 25° C.

The solution after being cooled and solidified in the air gap is coagulated into a filament yarn in a coagulating solution at a certain concentration and temperature. The lyocell fiber according to the present invention is controlled to have a pre-determined coagulation coefficient in the process of coagulating and thereby the lyocell fiber may have desired properties.

The condition factors may be expressed as a coagulation coefficient as a result of a mathematical function of the temperature of cooling air and the temperature of a coagulation bath, as shown below.

Coagulation Coefficient=T _(D) /T _(c) ,T _(D) =T _(D) +T _(A)−90

T_(D) means the temperature of a spinning solution, T_(A) means the temperature of cooling air applied in an air gap and T_(c) means the temperature of a coagulation bath. In the process of producing a lyocell fiber according to the present invention, the coagulation coefficient may be 0.8 to 1.3.

In order to adjust the coagulation coefficient, the concentration of the coagulation bath is adjusted in order that the concentration of NMMO is adjusted in the range of 5 to 20 wt %. In the range of 0.8 to 1.3 of coagulation coefficient, the temperature of the spinning solution and that of the coagulation bath become almost similar and the spreading rate of the NMMO contained in the spinning solution into the coagulation bath goes down as low as it can be. As a result, the homogeneous coagulation may be accomplished. Therefore, the section of a mono-filament constituting the multi-filament becomes very homogeneous and high strength is accomplished.

From the lyocell fiber produced according to the above-mentioned process, a greige cord is prepared and then a dip cord is prepared. The greige cord is prepared by twisting a certain number of ply twist yarn and cable twist yarn to two ply of lyocell fibers. Preferably, the twisting may be carried out at 300/300 TPM to 500/500 TPM for cable twist/ply twist and the number of ply twist yarn and cable twist yarn is not necessarily the same. The greige cord by twisting ply twist yarn and cable twist yarn is then dipped to a dipping solution. A dip cord for tire is prepared after a resin layer is attached to the greige cord.

The lyocell fiber for tire-cord according to the present invention has 800 to 3300 in denier of the entire fineness and 0.5 to 2.0 in denier of each monofilament fineness. The lyocell fiber produced by adjusting 0.8 to 1.3 in coagulation coefficient according to the present invention is characterized with following physical properties:

(1) 6.4 to 8.3 g/d in tenacity of the multi-filament,

(2) 5.7 to 7.1% in breaking elongation, and

(3) less than 2.5% in Coefficient of Variation of section diameter (CV(%))

The dip cord prepared according to the present invention is characterized with following physical properties:

(1) 4 to 6 g/d in tenacity,

(2) 5 to 10% in breaking elongation, and

(3) 70 to 100% in fatigue resistance

MODE FOR THE INVENTION

Hereinafter, the present invention will be described in detail with examples and comparative examples. These examples are provided only for the illustrative purpose, and it should not be construed that the scope of the invention is limited thereto.

According to the examples and comparative examples, the physical properties of the lyocell multi-filament are evaluated as following.

Tenacity (g/d) and Breaking Elongation (%)

The above-mentioned values were measured immediately after dried with a heat dryer for 2 hours at temperature of 107° C. The measurement was performed with a low-speed elongating tensile strength tester from Instrong LTD., USA and the conditions of measurement are as following:

80 Tpm (80 turns twist/m); 250 mm in length of sample; 300 m/min at speed.

Coefficient of Variation of Section Diameter (CV(%))

The above-mentioned value is calculated after each size of multi-filament and mono-filament is obtained by using a microscope. Coefficient of Variation of section diameter (CV(%)) is to determine the degree of relative dispersion and is calculated by dividing the standard deviation with the average value.

The physical properties of various lyocell fibers produced according to coagulation coefficient are shown in Table 1.

Fatigue Resistance (%)

Samples were subjected a fatigue test using a Goodrich disc fatigue tester which is conventionally used for the fatigue test of tire cords. Then, they were measured for residual strength, and fatigue resistances were compared. The fatigue test was conducted under the following conditions: 120° C., 2500 rpm, and 10% and 18% compression. After the fatigue test, the samples were dipped in tetrachloroethylene solution for 24 hours to swell rubber, and then, a cord was separated from the rubber and measured for residual strength. This residual strength was measured using a conventional tensile strength tester by the above-described measurement method (a), after drying at 107° C. for 2 hours.

EXAMPLES Example 1

A cellulose solution with 11.5 wt % in concentration was prepared by using a mixture of pulp powder with 1200 in degree of polymerization (containing 97% in contents of α-cellulose), NMMO.1H₂O and 0.01 wt % propyl gallate. A spinning nozzle that is 100 mm in diameter and has 1000 orifices with 150 μm in diameter was used to extrude the cellulose solution. In this case, the ratio of length to diameter (L/D) of each orifice was 4 in the spinning nozzle. The solution extruded from the spinning nozzle (head temperature at 100° C.) was exposed to a cooling air at 5° C. and 5 msec with 50 mm air gap and then the solution is spun wherein the amount of the extruded solution and the spinning speed were adjusted in order that the final filament fineness is 1000 denier. In this case, the temperature of coagulating solution was 15° C. in order that the coagulation coefficient is 1. The concentration of a coagulation bath was adjusted to 80% in water and 20% in NMMO, and then water-washed, dried and wound in order to obtain a filament yarn. Physical properties of the obtained filament are described in Table 1.

Example 2 and 3

A lyocell multi-filament was prepared by the same process as example 1, only except for changing the temperature of the cooling air in the air gap to 10° C. (for example 2) and 15° C. (for example 3), and the temperature of the coagulation bath to 20° C. (for example 2) and 25° C. (for example 3) in order that the coagulation coefficient is 1. Physical properties of the obtained filament are described in Table 1.

Example 4 to 6

A lyocell multi-filament was prepared by the same process as example 1, only except for changing the amount of the extruded solution and the spinning speed in order that the final filament fineness is 1500 denier. In this case, the temperature of the coagulating solution is adjusted in order that the coagulation coefficient is 1. Physical properties of the obtained filament are described in Table 1.

TABLE 1 breaking coagulation elongation fineness T_(D) T_(A) T_(D′) T_(c) coefficient Tenacity (g/d) (%) CV (%) Ex. 1 1000 d 100 5 15 15 1 7.3 6.8 0.7 Ex. 2 1000 d 100 10 20 20 1 7.8 7.1 0.9 Ex. 3 1000 d 100 15 25 25 1 8.3 5.9 1.4 Ex. 4 1500 d 110 5 25 25 1 7.0 5.7 2.1 Ex. 5 1500 d 110 10 30 30 1 7.4 6.6 1.7 Ex. 6 1500 d 110 15 35 35 1 6.4 6.1 1.8

COMPARATIVE EXAMPLES Comparative Example 1 and 2

A lyocell multi-filament was prepared by the same process as example 1, only except for changing the temperature of the coagulation bath to 20° C. (for comp. ex. 1) and 15° C. (for comp. ex. 2) in order that the coagulation coefficient is 0.75 (for comp. ex. 1) and 1.33 (for comp. ex. 2). Physical properties of the obtained filament are described in Table 2.

Comparative Example 3 and 4

A lyocell multi-filament was prepared by the same process as example 3 and 4, only except for changing the temperature of the coagulation bath to 10° C. (for comp. ex. 3) and 15° C. (for comp. ex. 4) in order that the coagulation coefficient is 2.5 (for comp. ex. 3) and 2.0 (for comp. ex. 4). Physical properties of the obtained filament are described in Table 2.

TABLE 2 coagulation Tenacity breaking elongation fineness T_(D) T_(A) T_(D′) T_(c) coefficient (g/d) (%) CV (%) Comp. Ex. 1 1000 d 100 5 15 20 0.75 6.3 5.8 2.7 Comp. Ex. 2 1000 d 100 10 20 15 1.33 6.2 6.1 2.9 Comp. Ex. 3 1500 d 110 5 25 10 2.5 6.0 5.7 3.1 Comp. Ex. 4 1500 d 110 10 30 5 2.0 5.4 5.6 2.7

Referring to Table 1, if the coagulation coefficient is adjusted to 1, the Coefficient of Variation of section diameter (CV(%)) decreases. Meanwhile, the coagulation coefficient is more or less than 1, the Coefficient of Variation of section diameter (CV(%)) is 2.7 and 2.9 in each comparative example, meaning that non-homogeneity of the size of mono-filament is increased as shown in Table 2. At the same time, the tenacity of multi-filament is reduced and the Coefficient of Variation of section diameter (CV(%)) is also increased, meaning that the homogeneity of the mono-filament is reduced. Examples 1 to 6 show the result of the Coefficient of Variation of section diameter (CV(%)) of lyocell multi-filament obtained by adjusting coagulation coefficient to 1. In reality, if the coagulation coefficient is adjusted to 0.8 to 1, a lyocell multi-filament with 2.5 or less in Coefficient of Variation of section diameter may be prepared.

INDUSTRIAL APPLICABILITY

The lyocell fiber according to the present invention may have suitable properties for using as a dip cord for tire cord. The Coefficient of Variation of section diameter (CV(%)) of the lyocell fiber is an important factor to determine the fatigue resistance of tire-cord. According to the present invention, the Coefficient of Variation of section diameter (CV(%)) may be controlled in the desired range by adjusting coagulation coefficient. Hence, the present invention has an advantage of producing a lyocell multi-filament for using as a dip cord for tire-cord. 

1. A process for producing a lyocell multi-filament in which the process includes preparing a spinning solution by homogenously dispersing, swelling and dissolving cellulose powder in a NMMO solution; spinning the spinning solution into an air gap through a spinning nozzle; and coagulating the extruded-spun spinning solution in a coagulation bath, characterized in that the coagulating is adjusted by means of a coagulation coefficient in the range of 0.8 to 1.3 and the coagulation coefficient is expressed as shown below, coagulation coefficient=T_(D)/T_(c), T_(D)=T_(D)+T_(A)−90; and T_(D), T_(A) and T_(c) mean the temperature of a spinning solution, the temperature of cooling air applied in an air gap and the temperature of a coagulation bath, respectively.
 2. The process of producing a lyocell multi-filament according to claim 1, wherein the coagulation coefficient is
 1. 3. The process of producing a lyocell multi-filament according to claim 1, wherein the temperature of the coagulation bath to 15 to 25° C.
 4. The process of producing a lyocell multi-filament according to claim 1, wherein the fineness of lyocell multi-filament is 800 to 3300 denier.
 5. The process of producing a lyocell multi-filament according to claim 1, wherein T_(D), T_(A), T_(D) and T_(c) are 100 to 110° C., 5 to 15° C., 15 to 35° C. and 15 to 35° C., respectively.
 6. A lyocell multi-filament for use of tire dip cord produced according to claim 1 and with following physical properties: 800 to 3300 denier in entire fineness; 0.5 to 2.0 denier in each monofilament fineness; 6.4 to 8.3 g/d in tenacity of the multi-filament, 5.7 to 7.1% in breaking elongation, and less than 2.5% in Coefficient of Variation of section diameter (CV(%)) 